1. Field of the Invention
This invention relates to a magnetic image recording and reproducing apparatus (what is called a time-lapse VTR) capable of reproducing images that are free of vertical wobbles even in continuous playback of a tape that was subjected to long-term recording with omission of fields.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. Hei. 6-197300 discloses an example of a time-lapse VTR in which a video signal is recorded with such omission of fields that only one field is recorded every three fields and playback is performed continuously. This publication relates to a gate means and a tape running control means for omitting fields. A conventional VTR will be described below which reduces the degree of vertical wobbles by employing the scheme of this publication.
FIG. 11 is a block diagram showing the configuration of an image signal processing apparatus for use in a conventional monitoring VTR, and FIG. 10 is a schematic diagram showing the arrangement of four heads on a rotary drum.
In FIG. 10, reference numeral 1 designates a rotary drum. Numerals 2a and 2b denote a pair of first heads which have different azimuth angles and are spaced apart from each other by 180.degree.. Numerals 3a and 3b denote a pair of second heads which have the same azimuth angles as the heads 2a and 2b, respectively, and are positioned ahead of the heads 2a and 2b by a distance corresponding to an integral multiple (in this embodiment, 2H) of one horizontal scanning period (hereinafter referred to as 1H) on a video track to be recorded on a magnetic tape by means of the first heads 2a and 2b.
Conventionally, monitoring of 18 hours with a VTR is performed in the following manner, for example., That is, with the use of a tape having a recording time of 120 minutes, a recording mode of the VTR is selected which has a recording time three times that of a six-hour recording mode (triple recording mode; hereinafter referred to as an EP mode). The six-hour recording mode is a recording mode in which the recording time is tripled from 2 hours of a standard recording mode (hereinafter referred to as an SP mode) having a VHS video standard tape feed rate by making both of the tape feed rate and the recording track width 1/3 of those of the SP mode.
To carry out 18-hour recording, only the tape feed rate is set at 1/3 of that of the EP mode and a tape is continuously run. A video signal is recorded on the tape once every three fields of the video signal by means of the pair of second heads 3a and 3b provided on the rotary drum 1. During playback of the video signal, while the tape is continuously fed at the same tape feed rate as that of the recording, that is, at a rate 1/3 that of the EP mode, the same record track is repeatedly reproduced by alternately using the heads that have the same azimuth angle and are spaced apart from each other by about 180.degree. (i.e., approximately opposed to each other) on the rotating drum 1.
At this time, to reproduce the same track three times, playback is performed such that the head 3a is used first, the head 2a having the same azimuth as the head 3a is then used, and the head 3a is thereafter used again. Since the head 2a is positioned behind the head 3b by a distance corresponding to a gap space in the drum rotational direction, a video signal reproduced by the head 2a lags from a video signal reproduced by the head 3a by a time corresponding to the gap space, for instance, 2H (see FIG. 12(c)). Unless this time lag is eliminated, images reproduced on a monitor will have vertical wobbles due to the 2H time lag of a V-sync signal (vertical synchronizing signal) corresponding to the gap space. To avoid this problem, a FM-demodulated image signal (video signal) obtained from a FM reproduction signal reproduced by the second head 3a is delayed by 2H with two cascade 1H delay circuits 7 and 8 (see FIG. 10). This is shown in FIG. 12(d).
Similarly, the same track is reproduced repeatedly such that the head 3b is used first, the head 2b having the same azimuth as the head 3b is then used, and the head 3b is thereafter used again. An image signal obtained with the use of the second head 3b is delayed by 2H. This is shown in FIG. 12(g).
The operation of each block shown in FIG. 11 will be described below. FM signals recorded field by field on a magnetic tape are reproduced by the pair of first heads 2a and 2b and the pair of second heads 3a and 3b. Selection between reproduced first field signals 21 and 24 and reproduced second field signals 23 and 22 is made in a head amplifier 4 based on a first head changeover signal having a 50% duty ratio that is produced by a first head changeover signal generation circuit 9. On the other hand, selection between outputs of the pair of first heads 2a and 2b and outputs of the pair of second heads 3a and 3b is made based on a second head changeover signal 26 that is produced by a second head changeover signal generation circuit 10. A selected reproduction signal is amplified by a head amplifier 4.
The selected and amplified FM reproduction signal is detected by an FM detection circuit 5, whereby a video signal 27 is obtained. This video signal 27 is delayed by two 1H-delay circuits 7 and 8 (for example, 1H CCD), to become a video signal 28 delayed by 2H. Both of the video signal 27 and the delayed video signal 28 are input to a switch 6. The switch 6 outputs either of the two received video signals on the basis of the second head changeover signal 26. Specifically, the switch 6 outputs the video signal 27 while the first head 2a or 2b is doing reproduction, and outputs the video signal 28 while the second head 2a or 2b is doing reproduction.
Referring to FIGS. 12 and 13, an explanation will be given of a case of reproducing FM signals that were alternately recorded at different azimuth angles on a magnetic tape by means of the pair of first heads 2a and 2b and the other pair of second heads 3a and 3b by continuously running the tape at a tape feed rate that is 1/3 of the tape feed rate of the EP mode.
FIG. 13 shows recorded recording tracks A and B on which FM signals are recorded by heads having different recording azimuth angles. Since FM signals are recorded once every three fields as mentioned above, they are recorded in the recording tracks A and B on the magnetic tape as shown in FIG. 13. At the time of playback, the FM signals are reproduced by tracing each of the tracks A and B three times.
The recording tracks A and B having different azimuth angles are traced as shown in FIG. 13. Specifically, the recording track A is traced by the heads 3a, 2a, and 3a in this order, and the recording track B is traced by the heads 3b, 2b, and 3b in this order. That is, the heads 2a and 2b trace the center line of each recording track, and the heads 3a and 3b trace both sides of the center line of each recording track. This reproducing operation can be controlled by a phase relationship between recording tracks and a control track signal (which is usually recorded at the lower end of the tape) which acts as a reference signal instead of V-sync signals of a recording signal.
As seen from FIG. 12, reproduction video signals 27 obtained from the FM signals of the recording tracks A and B are sequentially output from the FM detection circuit 5, and delayed by the 1H-delay circuits 7 and 8, to become delayed reproduction video signals 28. Both of-the video signals 27 and 28 are input to the switch 6, where the delayed reproduction video signals of the heads 3a and 3b (see FIGS. 12(d) and 12(g)) are selected based on the second head changeover signal 26.
When the recording tracks A and B are traced by the heads as shown in FIG. 13, the head 2a reproduction video signal and the head 3a delayed playback video signal are output from the switch 6 in connection with the recording track A, whereas the head 2b reproduction video signal and the head 3b delayed reproduction video signal are output from the switch 6 in connection with the recording track B. That is, the video signals are output in the order of the head 3a delayed reproduction video signal, the head 2a reproduction video signal, the head 3a delayed reproduction video signal, the head 3b delayed reproduction video signal, the head 2b reproduction video signal, the head 3b delayed reproduction video signal
Although the above description is directed to the case where the first heads 2a and 2b trace the center lines of respective recording tracks at the time of playback, the first heads 2a and 2b and the second heads 3a and 3b may be interchanged so that the centers of respective recording tracks are traced by the second heads 3a and 3b.
Since the conventional image recording and reproducing apparatus also capable of long-term recording is constructed as described above, it necessarily requires the 1H-delay circuits 7 and 8 and the switch 6. If the delay circuits 7 and 8 are implemented by a CCD (charge-coupled device), it will cause a cost increase. On the other hand, other types of delay elements have a problem of low accuracy of a delay time. Moreover, it is difficult to freely set a delay time in accordance with the gap spaces between the first heads 2a and 2b and the second heads 3a and 3b.
The conventional image recording and reproducing apparatus also capable of long-term recording copes with only vertical wobbles caused by the gap spaces of the magnetic heads. However, the conventional image recording and reproducing apparatus cannot completely eliminate, for instance, vertical wobbling of images due to so-called horizontal deviation which wobbling arises in reproducing the same track two or more times while a recorded tape in which positions of H-sync signals (horizontal synchronizing signals) of adjacent tracks recorded at the lower end of the magnetic are deviated from each other is continuously run at a given speed.
Furthermore, the conventional image recording and reproducing apparatus also capable of long-term recording cannot completely eliminate vertical wobbling of reproduced images on a monitor caused by a phenomenon that the delay time to be corrected depends on the linearity of a vertical scanning circuit of each monitor.